# Thread: keep having trouble with this..

1. ## keep having trouble with this..

Find the volume of the solid obtained by rotating the region bounded by the given curves about the specified axis.

y=20x–5x^2
y=0

How I started the problem was I solved the first equation and got [0,4]. And then I used these numbers and plugged it into the shell method.
The equation that I used for the shell method was the first one equation that I listed.

But, it's incorrect. Can someone show me how to setup and solve the problem?

2. Originally Posted by abilitiesz
Find the volume of the solid obtained by rotating the region bounded by the given curves about the specified axis.

y=20x–5x^2
y=0

How I started the problem was I solved the first equation and got [0,4]. And then I used these numbers and plugged it into the shell method.
The equation that I used for the shell method was the first one equation that I listed.

$V = 2\pi \int_0^4 x(20x-5x^2) \, dx = \frac{640\pi}{3}$